Priority based power-off during partial power loss

ABSTRACT

In one embodiment, a system includes a number of networking modules. Each module includes a respective voltage controller and a voltage-configuration circuit. The voltage-configuration circuit includes a number of transistors that are each coupled to a respective resistor. The system also includes one or more processors coupled to the voltage controllers including instructions executable by the processors. The processors being operable when executing the instructions to configure, for each module, an on-state or off-state of the transistors coupled to the respective resistor. The transistors coupled to the respective resistor correspond to a bit of a number of under-voltage thresholds. The processors are also operable to preset, during a module initialization, a relative ranking of under-voltage shutdown between the modules by setting the transistors. At least one of the number of networking modules has a different under-voltage threshold level relative to another one of the networking modules.

PRIORITY

This application claims the benefit, under 35 U.S.C. § 119(e), of U.S.Provisional Patent Application No. 62/317,406, filed 1 Apr. 2016, whichis incorporated herein by reference.

TECHNICAL FIELD

This disclosure generally relates to networking components.

BACKGROUND

A router (or router chassis) is a system that links computing devices tothe Internet and may operate by choosing the best path for data totraverse the Internet to its destination. The router may typicallyinclude a number of modules or cards, such as for example line cards,fabric cards, and management cards. The line cards provide ingress andegress packet processing functionalities, the fabric cards areresponsible for moving packets between the line cards, and themanagement cards execute the control plane software that is the userinterface to the switch or router.

The various cards may include a number of application-specificintegrated circuits (ASICs) designed for Ethernet switching and/orrouting typically have Ethernet ports to interact with other Ethernetswitches or routers. Each ASIC or groups of ASICs of the router may runits own Ethernet switching or routing stack. All the modules or cardsare powered by a common power bus or busses within the router. Forexample, a router may support the use of multiple power supplies thatcollectivity provide a 12 volt bus that powers the modules within therouter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example method for transmitting data betweenASICs.

FIG. 2 illustrates an example circuit that allows multiple configurablevoltage thresholds.

FIG. 3 illustrates an example method for configuring module power basedon a voltage-based ranking.

FIG. 4 illustrates an example system of networking cards with integratedline and fabric functionality.

FIG. 5 illustrates a networking card with integrated line and fabricfunctionality.

FIGS. 6-7 illustrate an example cable backplane enclosure with venttubes.

FIG. 8 illustrates an example computer system.

DESCRIPTION OF EXAMPLE EMBODIMENTS

High density, high throughput Ethernet switches and routers aretypically built using an application specific integrated circuit (ASIC).In a modular chassis switch or router where the number of ports exceedswhat a single ASIC can support, the switch or router may employ multipleASICs that all share the same architecture. These ASICs are usually partof a family of ASICs (e.g., developed by a single vendor) that may use aproprietary protocol to communicate, pass data, or generally cause themultiple ASICs to behave like a single switch or router. Future modules(e.g., a card) for the router may be constrained to using ASICs thatcommunicate using the same proprietary protocol in order to co-exist inthe router and be backwards-compatible with earlier modules. Theseconstraints may result in limiting the roadmap of a modular router to asingle ASIC architecture.

As described above, ASICs designed for Ethernet switching and/or routinghave Ethernet ports to interact with other Ethernet switches or routers.An ASIC is an integrated circuit (IC) that may be customized for aparticular purpose. In the case of a router or switch, a card or modulemay include ASICs may support Ethernet switching and routing protocols,and they may be designed to work in a network environment with otherEthernet switches and routers that may or may not share the sameunderlying architecture. The switches or routers may be interconnectedusing external cables or fibers running standard Ethernet protocols andeach switch or router may have its own control plane software thatmanages the switching and routing protocol stack. Although theembodiments may be described with regard to a particular type ofnetworking component, this disclosure contemplates any suitablenetworking component such as for an example network switches.

Particular embodiments provide a modular router where ASIC fromdifferent vendors that use different architecture may interoperate andcoexist in the router. Furthermore, an abstraction layer of softwarerunning on top of this modular chassis environment, hereinafter referredto as the platform, may cause the platform behave as a single instanceof a homogeneous switch or router. ASICs are usually built to support aspecific set of functions that benefit from being done in hardware vs.software, usually for speed or throughput. Different ASICs havingdifferent underlying architectures may be good in certain areas offunctions and not so good in others.

In particular embodiments, the platform includes a number ofheterogeneous ASICs that share standard Ethernet interfaces andprotocols, but differing from one another in their underlyingarchitecture. A network of these heterogeneous ASICs may be installedwithin the router or switch using Ethernet switching or routingprotocols and interconnected to each other through printed circuit board(PCB) traces, cables, fiber optics, and/or silicon photonics. Anabstraction layer of software may provide a uniform and unitaryinterface to this heterogeneous architecture, so that the set ofheterogeneous ASICs appears to be a single homogeneous switch or routerto higher levels of the software protocol stack. The abstractionsoftware may also simplify the complexity of the modular, multi-chipenvironment, such as, by way of example and not limitation, low-levelhardware monitoring and management of power, voltage, temperature, fanspeed, I²C signaling (e.g., over a multi-master, multi-slave,single-ended, or serial computer bus), peripheral component interconnectexpress (PCIe) signaling, present signal, etc.

As an example and not by way of limitation, a heterogeneous set of ASICsinside the modular router may include using a mix of switch ASICs withshallow packet buffers and switch ASICs with deep packet buffers.Shallow and deep buffer ASICs are examples of switch/routing ASIC typesthat may have different underlying architectures. A data packet is aformatted unit of data carried by a packet-switched network. Packetbuffers may be used at point where data packets get delayed. This delaymay occur when data packets are coming into an ASIC faster than the datapackets are transmitted by the ASIC. The packet buffers may queue thedata packets and deliver the data packets when a burst of data hassubsided. Without a packet buffer, some of the data packets would bedropped. The shallow-buffered ASICs may offer high density and bettercost-per-port, while the deep-buffered ASICs may offer better toleranceto transient congestion but at a higher cost per port. As anotherexample, the heterogeneous set of ASICs may include using a mix offixed-featured, purpose-built ASIC and programmable ASICs that can bereprogrammed to add new features. Fixed-featured, purpose-built ASICshave fixed functions and support only those functions, whileprogrammable ASICs are designed to be programmable so that the functionscan be changed through firmware or software configurations. While eacharchitecture has its advantages, these heterogeneous ASICs are normallyonly able to communicate with each other through use of a proprietaryheader to carry information between heterogeneous ASICs from the samefamily. By mixing ASICs in a single router and building an overlay, theadvantages of each type of ASICs may be combined without needingmultiple boxes or dealing with different operating systems.

In particular embodiments, the abstraction layer of software executed bya central process unit (CPU) of the router interfaces with theheterogeneous ASICs. The abstraction layer may configure theheterogeneous ASICs to switch or route data packets using a networkingprotocol, as described below. In particular embodiments, the abstractionlayer may configure the heterogeneous ASICs to establish a tunnelsupported by the standard networking protocols to move the data packetsbetween the heterogeneous ASICs. The tunneling protocol allows theabstraction layer to access or provide a service that the underlyingnetwork does not support or provide directly. The tunneling protocolembeds incoming packets into an additional header that is used to carryinformation on how to move the packets inside the router. In otherwords, the packets are encapsulated within another packet format nativeto the protocol stack of the destination ASIC. In particularembodiments, the additional header of a network protocol (e.g.,multiprotocol label switching (MPLS) or internet protocol-in-internetprotocol (IP in IP), as described below) is used to tunnel packets fromone ASIC to another ASIC within the chassis. The additional header maybe removed prior to the data packet being transmitted out of the routeror switch.

In particular embodiments, the abstraction layer of software may useMPLS to move data between one ASIC and another ASIC inside the router.MPLS is a type of data-carrying technique for high-performancetelecommunication networks that directs data from one network node tothe next based on short-path labels rather than long network addresses.The MPLS labels identify virtual links (paths) between distant nodesrather than endpoints. Information specific to the implementation may beembedded into the MPLS label(s). In particular embodiments, MPLSencapsulation may be used to carry data and implementation specificinformation from ASIC to/from the CPUs inside the chassis. As an exampleand not by way of limitation, the tunneling protocol may use a MPLSheader to embed information such as which ports in the router receivedthe data packet, which line card or ASIC is the destination for the datapacket, or which path within the chassis the packet should take. Thedata packet with the modified MPLS header may then be transmitted to itsdestination that may be a heterogeneous ASIC.

In particular embodiments of the abstraction layer of software may useIP-over-IP using Internet protocol version 4 (IPv4) as the tunnelingprotocol to move data between one heterogeneous ASIC to another withinthe router. IPv4 is a data protocol for use on packet-switched networksand an IPv4 data packet includes a header section and a data section. Inparticular embodiments, the information may be embedded in the IPv4address since the internal addresses within the router may be set by therouter. This information may include, for example, which ports in therouter received the data packet, which line card or ASIC is thedestination for the data packet, or which path within the chassis thepacket should take, as described above. In particular embodiments, oneor more IPv4 headers may be modified to include the information specificto the implementation. The difference in MPLS or IP-over-IP are the sizeof the header, and therefore the overhead; how widely adopted theprotocol is by ASIC vendors; and flexibility of the protocol tomanipulate the header and embed information in it, while still allowingASICs to parse and forward based on these headers.

In particular embodiments, data packets are redirected to CPUs withinthe chassis for further processing, and the MPLS header use to carrysimilar information plus other metadata that provides information to theabstraction layer executed on the CPU decide what to do with the datapacket when it receives it. Particular embodiments may provide atunneling method to extend the data plane from the chassis toservers/CPUs outside the chassis. A heterogeneous set of ASICs mayco-exist and operate in a single chassis through use of cable backplanetechnology, described below, to provide a Clos-fabric connectivity ofASICs without requiring specialized fabric cards or other transportprotocol to achieve the full non-blocking reachability of ASIC to ASIC.Because we know the connectivity of the ASICs inside the chassis, astatic, simplified version of these protocols may be used withoutburdening the software with full control plane implementation of theseprotocols like MPLS.

Particular embodiments may use the abstraction layer of software totransmit data from an ASIC located inside the router to a CPU thatresides outside the router (e.g., on a server). As an example and not byway of limitation, the data from the ASIC may be transmitted to banks ofexternal servers for more CPU intensive processing by other softwareapplications. In particular embodiments, MPLS encapsulation may be usedto transmit data and implementation specific information from ASICinside the chassis to CPUs outside the chassis. As an example and not byway of limitation, the additional MPLS header may be kept in the MPLSdata packet and the additional MPLS header may provide the abstractionlayer, executed on the CPU, additional information regarding handing ofthe data packet. When a standard tunneling protocol is used, theabstraction layer of software may parse the header and extract anyembedded information. Although the embodiments may be described withregard to particular types of tunneling protocols, this disclosurecontemplates any suitable data transfer protocol such as for examplelayer 2.

FIG. 1 illustrates an example method 100 for transmitting data betweenASICs. The method may begin at step 110, where the processor of therouter configures the ASICs to route data packets using a standardprotocol. At step 120, the processor configures the ASICs to set up atunnel, using the standard protocol, for moving data packets from oneASIC to another of the ASICs. At step 130, the processor implements asoftware overlay to facilitate interaction between the ASICs through thetunnel for moving the data packets. Particular embodiments may repeatone or more steps of the method of FIG. 1, where appropriate. Althoughthis disclosure describes and illustrates particular steps of the methodof FIG. 1 as occurring in a particular order, this disclosurecontemplates any suitable steps of the method of FIG. 1 occurring in anysuitable order. Moreover, although this disclosure describes andillustrates an example method for transmitting data between ASICsincluding the particular steps of the method of FIG. 1, this disclosurecontemplates any suitable method for transmitting data between ASICsincluding any suitable steps, which may include all, some, or none ofthe steps of the method of FIG. 1, where appropriate. Furthermore,although this disclosure describes and illustrates particularcomponents, devices, or systems carrying out particular steps of themethod of FIG. 1, this disclosure contemplates any suitable combinationof any suitable components, devices, or systems carrying out anysuitable steps of the method of FIG. 1.

Networking modules may be powered using a common power bus or busses. Asexample and not by way of limitation, a chassis or router may supportmultiple power supplies that collectivity provide a 12 volt bus thatpowers the modules within the router. A partial power-loss event mayoccur where some number, but not all, of the power supplies are unableto supply power to the modules (commonly known as “brownout”). Whenbrownout occurs, the amount of power provided by the remainingoperational power supplies may not be sufficient to support the currentload of the modules or cards of the router, and the system power busvoltage may drop. Each module may have a voltage controller that maypower-off the module when a certain under-voltage threshold is reached.As the voltage controller of the modules detects under-voltage andpower-off states, the current load on the power bus is reduced untileventually reaching a level that the remaining power supplies cansupport. The end result is a non-deterministic mix of modules that arepowered off. Even though the under-voltage threshold is typically set tothe same level on each module (or type of module), the actualunder-voltage threshold may be dependent on factors such as componentvalue tolerances (i.e. resistor or capacitor tolerances), currentconsumption of the module during the brownout event, or electricalcharacteristics of the power delivery path to the module.

In particular embodiments, a processor of the router may configure avoltage-based ranking of one or more modules in order to perform adeterministic power-off of modules during a brownout event. Avoltage-based ranking of modules may allow powering off lower-prioritymodules, while allowing higher-priority modules to remain operational.As an example and not by way of limitation, servers servinglower-priority traffic, such as internet browsing, may be connected to aparticular set of line cards, while other servers servinghigher-priority traffic, such as paid services, may be connected toanother set of line cards. In particular embodiments, the voltage-basedranking may be set based on a user's preference. In other words, theuser may pre-determine an order in which the modules power off during abrownout event. While software-based mechanisms may be implemented todetect brownout and perform priority based power-off, there is generallyminimal time between a brownout event to when under-voltage detectionbegins to trip leaving very little time for software to react and takeaction.

FIG. 2 illustrates an example circuit that allows multiple configurablevoltage thresholds. Particular embodiments may perform a priority basedpower-off of modules within a system during a partial power loss event.Particular embodiments may provide a voltage-threshold configurationcircuit 200 to configure multiple under-voltage thresholds for apre-determined order for powering-off modules within a system during abrownout event. Each module may implement a voltage controller 202 tomonitor voltage and perform powering-off the respective module. Inparticular embodiments, voltage-threshold configuration circuit 200 mayinclude resistors R3 and R4 that are coupled to a voltage divider byfield-effect transistors (FETs) Q1 and Q2, respectively. The coupling ofeither resistor R3 or R4 to the voltage divider adjusts theunder-voltage threshold. FETs Q1 and Q2 may be any suitable lowthreshold voltage, low on-resistance transistor and the input to FETs Q1and Q2 may be provided by the processor of the router to program eachmodule's under-voltage threshold. As illustrated in the example of FIG.2, output signal HS_UV_TRIP_PT is connected to a voltage monitoringinput of module voltage controller 202. As illustrated in the example ofFIG. 2, the power supply 12V_IN is coupled to resistors R1, R3, and R4.

As described above, resistors R1 and R2 form a voltage divider to setthe under-voltage threshold. As an example and not by way of limitation,resistors R1 and R2 may have a resistance of 39Ω and 5Ω, respectively.FETs Q1 and Q2 are configured to selectively adjust the under-voltagethreshold by adding resistor R3 or R4, respectively, to the voltagedivider formed by resistors R1 and R2. As an example and not by way oflimitation, resistors R3 and R4 may have a resistance of 300Ω and 650Ω,respectively. Input signals SET_HS_TRIP[0] and SET_HS_TRIP[1] areconnected to the processor of the router and allows the processor to setthe desired under-voltage threshold by turning on and turning off FETsQ1 or Q2. In this example four different thresholds may be supported andenabling the module to have a particular one of four possible power-offlevels. The number of power-off levels may be scaled by addingadditional combinations of FETs and resistors in parallel to FET Q1 andresistor R3. Essentially each combination of FETs and associatedresistors represent an additional bit in the total number of possiblestates (power-off levels). In particular embodiments, the voltage-basedranking is set through setting one or more resistors to the voltagedivider. The voltage-based ranking may be set through enabling/disablingone or more FETs Q1 and Q2, thereby adding/removing resistors to theeffective voltage divider.

In particular embodiments, power to a particular module may be turnedoff when a value of output signal HS_UV_TRIP_PT is lower than theunder-voltage threshold of the respective module set by the coupling ofresistors R1 or resistor R2 to the voltage-divider. The value of outputsignal HS_UV_TRIP_PT is a function of power supply voltage 12V_IN, theresistor divider that includes resistors R1, R2, and either resistor R3or R4, and FETs Q1, and Q2. In particular embodiments, modules set withthe lowest under-voltage threshold power-off last and those with thehighest under-voltage threshold power-off first during a brownout event.

FIG. 3 illustrates an example method 300 for configuring module powerbased on a voltage-based ranking. The method may begin at step 310,where the processor of the router configures, for each module, anon-state or off-state of the transistors coupled to a respectiveresistor of the voltage-configuration circuit. In particularembodiments, the transistors coupled to the respective resistorcorrespond to a bit of a plurality of a number of under-voltagethresholds, as described above. At step 320, the processor presets,during a module initialization, a relative ranking of under-voltageshutdown between the modules by setting the transistors. In particularembodiments, at least one of the networking modules has a differentunder-voltage threshold level relative to another one of the networkingmodules. Once the state of the FETs are set through input signalsSET_HS_TRIP[0] and SET_HS_TRIP[1], as illustrated in the example of FIG.2, during an initial configuration, the remaining steps may be performedthrough the voltage controller 202 and reacts in “hardware time” duringa brownout. Particular embodiments may repeat one or more steps of themethod of FIG. 3, where appropriate. Although this disclosure describesand illustrates particular steps of the method of FIG. 3 as occurring ina particular order, this disclosure contemplates any suitable steps ofthe method of FIG. 3 occurring in any suitable order. Moreover, althoughthis disclosure describes and illustrates an example method forconfiguring module power based on a voltage-based ranking including theparticular steps of the method of FIG. 3, this disclosure contemplatesany suitable method for configuring module power based on avoltage-based ranking including any suitable steps, which may includeall, some, or none of the steps of the method of FIG. 3, whereappropriate. Furthermore, although this disclosure describes andillustrates particular components, devices, or systems carrying outparticular steps of the method of FIG. 3, this disclosure contemplatesany suitable combination of any suitable components, devices, or systemscarrying out any suitable steps of the method of FIG. 3.

FIG. 4 illustrates an example system of networking cards with integratedline and fabric functionality. A modular Ethernet switch or routerchassis typically includes cards, fabric cards, and management cards.The line cards provide ingress and egress packet processingfunctionalities. The fabric cards are responsible for moving packetsbetween the line cards, and the management card runs the control planesoftware that the user interfaces with the switch or router. Particularembodiments describe a platform that includes a router with fabricfunctionality integrated with the line cards so no separate fabric cardsare used, as illustrated in the example of FIG. 4. In particularembodiments, a cable backplane 410 may be used to interconnect the ASICson the line cards 420 to form a Clos network within the chassis. Thecable backplane is used as a backbone to connect several printed circuitboards (PCBs) together to make up a complete network or computer system.

FIG. 5 illustrates a networking card with integrated line and fabricfunctionality. Integrating the ASICs with switch or fabric functionality504 into a networking (e.g., line) card 420 having ASICs linefunctionality 502 leads to higher power consumption per line card andhigher heat density (even though overall power/heat per router remainsthe same). This integration of ASICs 502-504 leads to more pins beingrequired to bring signals to/from line cards since there are more ASICs502-504 per line card to communicate. As described below, using a cablebackplane 410 and high density connectors solve the challenge ofbringing large number of high speed signals to/from cards 420 withfabric functionality to one another. Particular embodiments of a modularchassis may use one or more ASICs 502-504 to perform the switching androuting hardware functionalities. ASIC 502 performs the fabricfunctionality (fabric ASIC), as well as ASIC 504 that performs theswitching/routing functionally (switch ASIC), may both be integratedinto a line card 420. In particular embodiments, fabric ASICs 502 andswitch ASICs 504 are interconnected to the fabric ASICs 502 and lineASICs 504 on other line cards 420 of the router via the cable backplaneto form a Clos network. A Clos network provides full connectivitybetween the ASICs 502-504. The Clos network provides a trade-off betweenblocking probability of data losses for a group of identical parallelresources versus cost/complexity.

FIGS. 6-7 illustrate an example cable backplane enclosure with venttubes. The cable backplane 410 may include a number of copper cables(e.g., micro coaxial cables) to interconnect the various cards 420 inthe router. The cables of the cable backplane may be bundled togetherand put inside an enclosure for easier handling, as described below.Each end of the cables terminate in electrical connectors 610 thatconnect the high-speed signals from one line card 420 to another and tomanagement cards. The assembly consisting of the cables and theenclosure forms a cable backplane module 410. Cables of cable backplane410 have much lower signal loss than PCB traces and therefore may handlehigher speed for longer distances. The enclosure may block airflowsimilar to traditional PCB in environments where front to back or backto front airflow is desirable (e.g., within a rack mount system). Inparticular embodiments, the enclosure may include one or more vent tube620 to direct air efficiently through the tray for enhanced airflow inorder to cool the line cards 420 coupled to cable backplane 410. Venttubes 620 provide guided tunnels for air to flow unimpeded through theenclosure.

FIG. 8 illustrates an example computer system 800. In particularembodiments, one or more computer systems 800 perform one or more stepsof one or more methods described or illustrated herein. In particularembodiments, one or more computer systems 800 provide functionalitydescribed or illustrated herein. In particular embodiments, softwarerunning on one or more computer systems 800 performs one or more stepsof one or more methods described or illustrated herein or providesfunctionality described or illustrated herein. Particular embodimentsinclude one or more portions of one or more computer systems 800.Herein, reference to a computer system may encompass a computing device,and vice versa, where appropriate. Moreover, reference to a computersystem may encompass one or more computer systems, where appropriate.

This disclosure contemplates any suitable number of computer systems800. This disclosure contemplates computer system 800 taking anysuitable physical form. As example and not by way of limitation,computer system 800 may be an embedded computer system, a system-on-chip(SOC), a single-board computer system (SBC) (such as, for example, acomputer-on-module (COM) or system-on-module (SOM)), a desktop computersystem, a laptop or notebook computer system, an interactive kiosk, amainframe, a mesh of computer systems, a mobile telephone, a personaldigital assistant (PDA), a server, a tablet computer system, or acombination of two or more of these. Where appropriate, computer system800 may include one or more computer systems 800; be unitary ordistributed; span multiple locations; span multiple machines; spanmultiple data centers; or reside in a cloud, which may include one ormore cloud components in one or more networks. Where appropriate, one ormore computer systems 800 may perform without substantial spatial ortemporal limitation one or more steps of one or more methods describedor illustrated herein. As an example and not by way of limitation, oneor more computer systems 800 may perform in real time or in batch modeone or more steps of one or more methods described or illustratedherein. One or more computer systems 800 may perform at different timesor at different locations one or more steps of one or more methodsdescribed or illustrated herein, where appropriate.

In particular embodiments, computer system 800 includes a processor 802,memory 804, storage 806, an input/output (I/O) interface 808, acommunication interface 810, and a bus 812. Although this disclosuredescribes and illustrates a particular computer system having aparticular number of particular components in a particular arrangement,this disclosure contemplates any suitable computer system having anysuitable number of any suitable components in any suitable arrangement.

In particular embodiments, processor 802 includes hardware for executinginstructions, such as those making up a computer program. As an exampleand not by way of limitation, to execute instructions, processor 802 mayretrieve (or fetch) the instructions from an internal register, aninternal cache, memory 804, or storage 806; decode and execute them; andthen write one or more results to an internal register, an internalcache, memory 804, or storage 806. In particular embodiments, processor802 may include one or more internal caches for data, instructions, oraddresses. This disclosure contemplates processor 802 including anysuitable number of any suitable internal caches, where appropriate. Asan example and not by way of limitation, processor 802 may include oneor more instruction caches, one or more data caches, and one or moretranslation lookaside buffers (TLBs). Instructions in the instructioncaches may be copies of instructions in memory 804 or storage 806, andthe instruction caches may speed up retrieval of those instructions byprocessor 802. Data in the data caches may be copies of data in memory804 or storage 806 for instructions executing at processor 802 tooperate on; the results of previous instructions executed at processor802 for access by subsequent instructions executing at processor 802 orfor writing to memory 804 or storage 806; or other suitable data. Thedata caches may speed up read or write operations by processor 802. TheTLBs may speed up virtual-address translation for processor 802. Inparticular embodiments, processor 802 may include one or more internalregisters for data, instructions, or addresses. This disclosurecontemplates processor 802 including any suitable number of any suitableinternal registers, where appropriate. Where appropriate, processor 802may include one or more arithmetic logic units (ALUs); be a multi-coreprocessor; or include one or more processors 802. Although thisdisclosure describes and illustrates a particular processor, thisdisclosure contemplates any suitable processor.

In particular embodiments, memory 804 includes main memory for storinginstructions for processor 802 to execute or data for processor 802 tooperate on. As an example and not by way of limitation, computer system800 may load instructions from storage 806 or another source (such as,for example, another computer system 800) to memory 804. Processor 802may then load the instructions from memory 804 to an internal registeror internal cache. To execute the instructions, processor 802 mayretrieve the instructions from the internal register or internal cacheand decode them. During or after execution of the instructions,processor 802 may write one or more results (which may be intermediateor final results) to the internal register or internal cache. Processor802 may then write one or more of those results to memory 804. Inparticular embodiments, processor 802 executes only instructions in oneor more internal registers or internal caches or in memory 804 (asopposed to storage 806 or elsewhere) and operates only on data in one ormore internal registers or internal caches or in memory 804 (as opposedto storage 806 or elsewhere). One or more memory buses (which may eachinclude an address bus and a data bus) may couple processor 802 tomemory 804. Bus 812 may include one or more memory buses, as describedbelow. In particular embodiments, one or more memory management units(MMUs) reside between processor 802 and memory 804 and facilitateaccesses to memory 804 requested by processor 802. In particularembodiments, memory 804 includes random access memory (RAM). This RAMmay be volatile memory, where appropriate. Where appropriate, this RAMmay be dynamic RAM (DRAM) or static RAM (SRAM). Moreover, whereappropriate, this RAM may be single-ported or multi-ported RAM. Thisdisclosure contemplates any suitable RAM. Memory 804 may include one ormore memories 804, where appropriate. Although this disclosure describesand illustrates particular memory, this disclosure contemplates anysuitable memory.

In particular embodiments, storage 806 includes mass storage for data orinstructions. As an example and not by way of limitation, storage 806may include a hard disk drive (HDD), a floppy disk drive, flash memory,an optical disc, a magneto-optical disc, magnetic tape, or a UniversalSerial Bus (USB) drive or a combination of two or more of these. Storage806 may include removable or non-removable (or fixed) media, whereappropriate. Storage 806 may be internal or external to computer system800, where appropriate. In particular embodiments, storage 806 isnon-volatile, solid-state memory. In particular embodiments, storage 806includes read-only memory (ROM). Where appropriate, this ROM may bemask-programmed ROM, programmable ROM (PROM), erasable PROM (EPROM),electrically erasable PROM (EEPROM), electrically alterable ROM (EAROM),or flash memory or a combination of two or more of these. Thisdisclosure contemplates mass storage 806 taking any suitable physicalform. Storage 806 may include one or more storage control unitsfacilitating communication between processor 802 and storage 806, whereappropriate. Where appropriate, storage 806 may include one or morestorages 806. Although this disclosure describes and illustratesparticular storage, this disclosure contemplates any suitable storage.

In particular embodiments, I/O interface 808 includes hardware,software, or both, providing one or more interfaces for communicationbetween computer system 800 and one or more I/O devices. Computer system800 may include one or more of these I/O devices, where appropriate. Oneor more of these I/O devices may enable communication between a personand computer system 800. As an example and not by way of limitation, anI/O device may include a keyboard, keypad, microphone, monitor, mouse,printer, scanner, speaker, still camera, stylus, tablet, touch screen,trackball, video camera, another suitable I/O device or a combination oftwo or more of these. An I/O device may include one or more sensors.This disclosure contemplates any suitable I/O devices and any suitableI/O interfaces 808 for them. Where appropriate, I/O interface 808 mayinclude one or more device or software drivers enabling processor 802 todrive one or more of these I/O devices. I/O interface 808 may includeone or more I/O interfaces 808, where appropriate. Although thisdisclosure describes and illustrates a particular I/O interface, thisdisclosure contemplates any suitable I/O interface.

In particular embodiments, communication interface 810 includeshardware, software, or both providing one or more interfaces forcommunication (such as, for example, packet-based communication) betweencomputer system 800 and one or more other computer systems 800 or one ormore networks. As an example and not by way of limitation, communicationinterface 810 may include a network interface controller (NIC) ornetwork adapter for communicating with an Ethernet or other wire-basednetwork or a wireless NIC (WNIC) or wireless adapter for communicatingwith a wireless network, such as a WI-FI network. This disclosurecontemplates any suitable network and any suitable communicationinterface 810 for it. As an example and not by way of limitation,computer system 800 may communicate with an ad hoc network, a personalarea network (PAN), a local area network (LAN), a wide area network(WAN), a metropolitan area network (MAN), or one or more portions of theInternet or a combination of two or more of these. One or more portionsof one or more of these networks may be wired or wireless. As anexample, computer system 800 may communicate with a wireless PAN (WPAN)(such as, for example, a BLUETOOTH WPAN), a WI-FI network, a WI-MAXnetwork, a cellular telephone network (such as, for example, a GlobalSystem for Mobile Communications (GSM) network), or other suitablewireless network or a combination of two or more of these. Computersystem 800 may include any suitable communication interface 810 for anyof these networks, where appropriate. Communication interface 810 mayinclude one or more communication interfaces 810, where appropriate.Although this disclosure describes and illustrates a particularcommunication interface, this disclosure contemplates any suitablecommunication interface.

In particular embodiments, bus 812 includes hardware, software, or bothcoupling components of computer system 800 to each other. As an exampleand not by way of limitation, bus 812 may include an AcceleratedGraphics Port (AGP) or other graphics bus, an Enhanced Industry StandardArchitecture (EISA) bus, a front-side bus (FSB), a HYPERTRANSPORT (HT)interconnect, an Industry Standard Architecture (ISA) bus, an INFINIBANDinterconnect, a low-pin-count (LPC) bus, a memory bus, a Micro ChannelArchitecture (MCA) bus, a Peripheral Component Interconnect (PCI) bus, aPCI-Express (PCIe) bus, a serial advanced technology attachment (SATA)bus, a Video Electronics Standards Association local (VLB) bus, oranother suitable bus or a combination of two or more of these. Bus 812may include one or more buses 812, where appropriate. Although thisdisclosure describes and illustrates a particular bus, this disclosurecontemplates any suitable bus or interconnects.

Herein, a computer-readable non-transitory storage medium or media mayinclude one or more semiconductor-based or other integrated circuits(ICs) (such, as for example, field-programmable gate arrays (FPGAs) orapplication-specific ICs (ASICs)), hard disk drives (HDDs), hybrid harddrives (HHDs), optical discs, optical disc drives (ODDs),magneto-optical discs, magneto-optical drives, floppy diskettes, floppydisk drives (FDDs), magnetic tapes, solid-state drives (SSDs),RAM-drives, SECURE DIGITAL cards or drives, any other suitablecomputer-readable non-transitory storage media, or any suitablecombination of two or more of these, where appropriate. Acomputer-readable non-transitory storage medium may be volatile,non-volatile, or a combination of volatile and non-volatile, whereappropriate.

Herein, “or” is inclusive and not exclusive, unless expressly indicatedotherwise or indicated otherwise by context. Therefore, herein, “A or B”means “A, B, or both,” unless expressly indicated otherwise or indicatedotherwise by context. Moreover, “and” is both joint and several, unlessexpressly indicated otherwise or indicated otherwise by context.Therefore, herein, “A and B” means “A and B, jointly or severally,”unless expressly indicated otherwise or indicated otherwise by context.

The embodiments disclosed above are only examples, and the scope of thisdisclosure is not limited to them. Particular embodiments may includeall, some, or none of the components, elements, features, functions,operations, or steps of the embodiments disclosed above. Embodimentsaccording to the invention may be directed to a method, a storagemedium, a system and a computer program product, wherein any featurementioned in one claim category, e.g. method, can be claimed in anotherclaim category, e.g. system, as well. The subject-matter which can beclaimed comprises not only the combinations of features as set out inthe attached claims but also any other combination of features in theclaims, wherein each feature mentioned in the claims can be combinedwith any other feature or combination of other features in the claims.Furthermore, any of the embodiments and features described or depictedherein can be claimed in a separate claim and/or in any combination withany embodiment or feature described or depicted herein or with any ofthe features of the aforementioned claims.

The scope of this disclosure encompasses all changes, substitutions,variations, alterations, and modifications to the example embodimentsdescribed or illustrated herein that a person having ordinary skill inthe art would comprehend. The scope of this disclosure is not limited tothe example embodiments described or illustrated herein. Moreover,although this disclosure describes and illustrates respectiveembodiments herein as including particular components, elements,feature, functions, operations, or steps, any of these embodiments mayinclude any combination or permutation of any of the components,elements, features, functions, operations, or steps described orillustrated anywhere herein that a person having ordinary skill in theart would comprehend. Furthermore, reference in any claims to anapparatus or system or a component of an apparatus or system beingadapted to, arranged to, capable of, configured to, enabled to, operableto, or operative to perform a particular function encompasses thatapparatus, system, component, whether or not it or that particularfunction is activated, turned on, or unlocked, as long as thatapparatus, system, or component is so adapted, arranged, capable,configured, enabled, operable, or operative. Additionally, although thisdisclosure describes or illustrates particular embodiments as providingparticular advantages, particular embodiments may provide none, some, orall of these advantages.

What is claimed is:
 1. A system comprising: a plurality of networkingmodules, wherein each module comprising a respective voltage controllerand a voltage-configuration circuit, and wherein thevoltage-configuration circuit comprises a plurality of transistors thatare each coupled to a respective resistor; and one or more processorscoupled to the voltage controllers comprising instructions executable bythe processors, the processors being operable when executing theinstructions to: configure, for each module, an on-state or off-state ofthe transistors coupled to the respective resistor, wherein thetransistors coupled to the respective resistor correspond to a bit of aplurality of under-voltage thresholds; and preset, during a moduleinitialization, a relative ranking of under-voltage shutdown between themodules by setting the transistors, wherein at least one of theplurality of networking modules has a different under-voltage thresholdlevel relative to another one of the networking modules.
 2. The systemof claim 1, wherein the resistors, transistors, and a voltage controllerreact independently to turn off power to the respective networkingmodule during a brownout based on the under-voltage threshold determinedby a state of the transistors.
 3. The system of claim 1, wherein theprocessors are further operable to couple one or more resistors to aresistor divider.
 4. The system of claim 3, wherein data of a powersupply voltage is a function of the power supply voltage and a value ofthe resistor divider.
 5. The system of claim 1, wherein the processorsare further operable to transmit a signal turning on the transistor thatis coupled to a respective resistor and a node of a voltage divider. 6.The system of claim 1, wherein the networking modules with a highestunder-voltage threshold are turned off before networking modules with alower under-voltage threshold.
 7. The system of claim 1, wherein theplurality of networking modules comprises a line card, fabric card, ormanagement card.
 8. One or more computer-readable non-transitory storagemedia embodying software that is operable when executed to: configure,for each of a plurality of networks modules, an on-state or off-state ofa plurality of transistors coupled to a respective resistor, wherein thetransistors coupled to the respective resistor correspond to a bit of aplurality of a number of under-voltage thresholds; and preset, during amodule initialization, a relative ranking of under-voltage shutdownbetween the modules by setting the transistors, wherein at least one ofthe plurality of networking modules has a different under-voltagethreshold level relative to another one of the networking modules. 9.The media of claim 8, wherein the resistors, transistors, and a voltagecontroller react independently to turn off power to the respectivenetworking module during a brownout based on the under-voltage thresholddetermined by a state of the transistors.
 10. The media of claim 8,wherein the software is further operable to couple one or more resistorsto a resistor divider.
 11. The media of claim 10, wherein data of apower supply voltage is a function of the power supply voltage and avalue of the resistor divider.
 12. The media of claim 8, wherein thesoftware is further operable to transmit a signal turning on thetransistor that is coupled to a respective resistor and a node of avoltage divider.
 13. The media of claim 8, wherein the networkingmodules with a highest under-voltage threshold are turned off beforenetworking modules with a lower under-voltage threshold.
 14. The mediaof claim 8, wherein the plurality of networking modules comprises a linecard, fabric card, or management card.
 15. A method comprising:configuring, for each of a plurality of networks modules, an on-state oroff-state of a plurality of transistors coupled to a respectiveresistor, wherein the transistors coupled to the respective resistorcorrespond to a bit of a plurality of under-voltage thresholds; andpresetting, during a module initialization, a relative ranking ofunder-voltage shutdown between the modules by setting the transistors,wherein at least one of the plurality of networking modules has adifferent under-voltage threshold level relative to another one of thenetworking modules.
 16. The method of claim 15, wherein the resistors,transistors, and the voltage controller react independently to turn offpower to the respective networking module during a brownout based on theunder-voltage threshold determined by a state of the transistors. 17.The method of claim 15, wherein further comprising coupling one or moreresistors to a resistor divider.
 18. The method of claim 17, whereindata of a power supply voltage is a function of the power supply voltageand a value of the resistor divider.
 19. The method of claim 15, furthercomprising transmitting a signal turning on the transistor that iscoupled to a respective resistor and a node of a voltage divider. 20.The method of claim 15, wherein the networking modules with a highestunder-voltage threshold are turned off before networking modules with alower under-voltage threshold.